The present invention relates in general to cylinder type key locks, and more particularly to key-operated rotary plug cylinder locks having rotary disk type tumblers incorporating special provisions to protect the lock against unauthorized operation by forcing of the lock with torquing tools and the like and constructed so as to resist detection of the combination or operation by picking probes or the like.
One of the common types of key locks which have come into wide use is the type known as a cylinder lock. Conventional cylinder locks normally comprise a relatively fixed cylinder forming the lock body or casing having a cylindrical bore opening through the front surface of the lock body which rotatably houses a rotating plug assembly. The rotating plug assembly has a keyway or key slot opening through the front surface of the plug and extending over most of the axial length of the plug, as well as one or more resiliently urged tumblers formed of rotatble or slidable members which normally occupy positions confronting or transversing shear planes or interfacial planes preventing rotation of the plug relative to the cylinder. When a key of proper contour or combination surface is inserted in the keyway or key opening in the plug, the contoured key surface aligns the resiliently urged tumbler members in such a way that a parting line, either of the tumbler members or of some other locking member coactive with the tumbler members, is brought into coincidence with the interfacial plane or the arcuate peripheral surface of the plug, so that when all of the resiliently urged tumblers are properly aligned by the contoured key surface, rotational motion imparted to the key permits the plug to turn through the normal motion involved in moving the lock from a locked to an unlocked condition.
Due to conditions which arise in the construction of the lock parts under normal manufacturing tolerances, it has been possible in cylinder locks which are not provided with special pick resistant features, to achieve unauthorized operation of the lock by such picking techniques as inserting a picking tool into the keyway and exerting a torque on the plug so that with careful movement of the plug in selected directions, the resiliently urged tumbler first placed in compression by torquing the plug is aligned by the pick for clearance, at which point the plug rotates a minute degree to bring the next resiliently urged tumbler into a similar compressed condition and is aligned by the pick for clearance, and this succession of operations is repeated until all of the tumblers have been aligned to permit the plug to be rotated.
One of the most common types of cylinder locks is the pin-tumbler type cylinder lock, wherein segmented tumbler pins formed of lower key-engaging pin segments and upper drive pin segments have a line of separation between the segments which is normally displaced from the shear line of the plug but is positioned by the proper key so that the line of separation of all of the pin tumblers align with the plug shear line and permit rotation of the plug. Such pin-tumbler type cylinder locks have been particularly susceptible to the above described types of picking techniques, and many attempts have been made to provide them with resistance to such picking operations.
To increase resistance to picking by the techniques which have been successfull with pin-tumbler type cylinder locks, cylinder locks of the rotary disk tumbler type have come into wider use. A popular type of rotary disk tumbler cylinder lock is one wherein a bank of peripherally gated rotary locking disks housed within a rotatable sleeve member have shaped center apertures which repsond to a proper key surface to align the gates to permit radially inward movement of a locking bar which normally traverses the shear line between the rotary sleeve and an outer fixed cylinder casing. Examples of rotary disk tumbler type cylinder locks of this type are found in U.S. Pat. Nos. 3,771,340, 3,621,689 and 3,848,442. Unauthorized detection of such rotary disk tumbler cylinder locks has been achieved, however, by techniques such as introducing a picking probe or similar tool into the key opening to interpose a radial extension of the shank of the probe between the faces of successive rotary disk tumblers and manipulating the probe to feel with the end of the radial extension the positions of the peripheral gates in the rotary disk tumblers which receive the locking bar to permit its movement to unlocking position. By observing the angular position of the probe externally of the lock at the positions at which the gates are felt, one can determine therefrom the key combination or shaped surface contour of the key for the lock. Also, introduction of a torquing tool into the plug of such locks to apply sufficient force to distort or jam relatively thinner components of the lock works into normally unoccupied spaces within the lock and force the locking bar into the slot therefor in the plug sleeve has resulted in unauthorized penetration of the lock.
An object of the present invention is the provision of a novel rotary plug cylinder lock having rotary disk type tumblers constructed to resist unauthorized detection of the key combination for the lock and resist unauthorized penetration of the lock by torquing techniques.
Another object of the present invention is the provision of rotary plug cylinder locks of the type described in the preceding paragraph, wherein disabling features are incorporated in the lock to prevent penetration or unauthorized operation of the lock when the plug is subjected to excessive stresses in certain directions.
Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings illustrating a preferred embodiment of the invention.